BACKGROUND OF THE INVENTION
1. Field of the Invention:
[0001] The present invention relates to earth-boring bits of the rolling cutter variety.
Specifically, the present invention relates to the cutting structure of earth-boring
bits of the rolling cutter variety.
2. Background Information:
[0002] The success of rotary drilling enabled the discovery of deep oil and gas reserves.
The rotary rock bit was an important invention that made that success possible. only
soft formations could be commercially penetrated but with the earlier drag bit, but
the original rolling-cone rock bit invented by Howard R. Hughes, U.S. Patent No. 939,759,
drilled the hard caprock at the spindletop field, near Beaumont Texas, with relative
ease.
[0003] That venerable invention, within the first decade of this century, could drill a
scant fraction of the depth and speed of the modern rotary rock bit. If the original
Hughes bit drilled for hours, the modern bit drills for days. Bits today often drill
for miles. Many individual improvements have contributed to the impressive overall
improvement in the performance of rock bits.
[0004] Rolling-cone earth-boring bits generally employ cutting elements on the cutters to
induce high contact stresses in the formation being drilled as the cutters roll over
the bottom of the borehole during drilling operation. These stresses cause the rock
to fail, resulting in disintegration and penetration of the formation material being
drilled. Conventionally, the cutters roll on axes that are offset, or do not coincide
with the geometric or rotational axis of the bit. Offset cutters do not purely roll
over the bottom of the borehole, but also slide, imparting a gouging and scraping
action to the cutting elements, in addition to the crushing mode of disintegration
of formation material.
[0005] Shear cutting is a disintegration mode that is not taken maximum advantage of in
the rolling-cutter earth-boring bit field as it is in the fixed-cutter or drag bit
field. Shearing formation material is the dominant disintegration mode in fixed-cutter
or drag bits, which commonly employ super-hard, highly wear-resistant cutting elements
to shear formation material at the bottom and sidewall of the borehole.
[0006] Commonly assigned U.S. patent No. 5,287,936, February 22, 1994 to Grimes et al. discloses
a shear-cutting gage cutting structure for earth-boring bits of the rolling cutter
variety. U.S. Patent No. 5,282,512 discloses cutting elements for a rolling cutter
bit with diamond-charged elements on the forward and central zones of the cutting
elements to enhance the shearing or scraping mode of formation disintegration. As
shown by U.S. Patent No. 5,287,936, the shearing mode of disintegration is particularly
advantageous employed at the corner and the sidewall of the borehole, where the gage
or diameter of the borehole is defined. Maintenance of a full gage or diameter borehole
is important to avoid sticking of the bit or other downhole equipment and to avoid
the necessity of reaming operations to restore the borehole to the full gage or diameter
condition.
[0007] A need exists, therefore, for earth-boring bits of the rolling-cutter variety having
cutting structures that take advantage of the shearing mode of formation disintegration
in addition to the crushing and gouging modes. It is a general object of the present
invention to provide an earth-boring bit having a cutting structure adapted to shearingly
engage formation material during drilling operation.
SUMMARY OF THE INVENTION
[0008] It is a general object of the present invention to provide an earth-boring bit of
rolling cutter variety having a cutting structure with heel cutting elements adapted
to shearingly engage formation material during drilling operation.
[0009] This and other objects of the present invention are accomplished by providing an
earth-boring bit having a bit body and at least one cantilevered bearing shaft depending
inwardly and downwardly from the bit body. A cutter is mounted for rotation on the
bearing shaft and includes a plurality of cutting elements arranged in generally circumferential
rows including an outer or heel row of cutting elements. At least one of the cutting
elements in the heel row has an outer surface at least partially formed of super-hard
material that defines a cutting edge for shearing engagement with the sidewall of
the borehole as the cutters roll and slide over the bottom of the borehole during
drilling operations.
[0010] According to the preferred embodiment of the present invention, the super-hard portion
is polycrystalline diamond and the remainder of the cutting element is formed of cemented
tungsten carbide, and the element is interference fit into an aperture in the cutter
surface.
[0011] According to the preferred embodiment of the present invention, the super-hard portion
of the outermost surface projects beyond the remainder of the outer end for engagement
with the sidewall of the borehole.
[0012] According to the preferred embodiment of the present invention, each of the heel
row cutting elements has an inner end, an outer end, and a crest. The portion of the
outer end formed of super-hard material is flush with or recessed from the crest of
the cutting element to define the shear cutting edge. The inner end and crest are
formed of fracture-tough hard metal to withstand the impact loads encountered by the
cutting element in the crushing mode of operation.
DESCRIPTION OF THE DRAWINGS
[0013] Figure 1 is a perspective view of an earth-boring bit according to the present invention.
[0014] Figure 2 is an elevation view of a heel cutting element of the earth-boring bit of
Figure 1.
[0015] Figure 3 is a plan view of the cutting element of Figure 2.
[0016] Figure 4 is an elevation view of another embodiment of the heel cutting element according
to the present invention.
[0017] Figure 5 is an elevation view of a heel cutting element according to the present
invention.
[0018] Figure 6 is a plan view of the cutting element of Figure 5.
[0019] Figure 7 is an elevation view of a heel cutting element according to the present
invention.
[0020] Figure 8 is a plan view of the cutting element of Figure 7.
[0021] Figure 9 is an elevation view of a heel cutting element according to the present
invention.
[0022] Figure 10 is a plan view of the cutting element of Figure 9.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] Referring now to the Figures, and particularly to Figure 1, an earth-boring bit
11 according to the present invention is illustrated. Bit
11 includes a bit body
13, which is threaded at its upper extent
15 for connection into a drillstring. Each leg or section of bit
11 is provided with a lubricant compensator
17, a preferred embodiment of which is disclosed in U.S. Patent No. 4,276,946, July
7, 1981 to Millsapps. At least one nozzle
19 is provided in bit body
13 to spray drilling fluid from within the drillstring to cool and lubricate bit
11 during drilling operation. Three cutters,
21,
23,
25 are rotatably secured to a bearing shaft associated with each leg of bit body
13. Each cutter
21,
23,
25 has a cutter shell surface including a gage surface
31 and a heel surface
41.
[0024] A plurality of cutting elements, in the form of hard metal inserts, are arranged
in generally circumferential rows on each cutter. Each cutter
21,
23,
25 has a gage surface
31 with a row of gage elements
33 thereon. A heel surface
41 intersects each gage surface
31 and has at least one row of heel inserts
43 thereon. At least one scraper element
51 is secured to the cutter shell surface generally at the intersection of gage and
heel surfaces
31, 41 and generally intermediate a pair of heel inserts
43.
[0025] The outer cutting structure, comprising heel cutting elements
43, gage cutting elements
33, and a secondary cutting structure in the form of scraper elements
51, combine and cooperate to crush and scrape formation material at the corner and sidewall
of the borehole as cutters
21,
23,
25 roll and slide over the formation material during drilling operation. The primary
cutting structure accomplishing this task is the outer ends of heel cutting elements
43, while scraper cutting elements
51 form a secondary cutting structure assisting the heel elements
43. As the outermost surfaces of heel cutting elements
43 wear, gage cutting elements
33 engage the sidewall of the borehole to maintain qage diameter. The wear resistance
and cutting efficiency of heel cutting elements
43 is enhanced by forming a portion of the outer end or outermost surface of elements
43 of a super-hard material defining a cutting edge for shearing engagement with the
sidewall of the borehole, as depicted in greater detail in Figures 2, 3, and 4.
[0026] Figures 2 and 3 are elevation and plan views, respectively, of a heel cutting element
43 according to the preferred embodiment of the present invention. Cutting element
43 comprises a generally cylindrical element body
61, which is preferably formed of a hard metal such as cemented tungsten carbide and
is secured by interference fit in the cutter shell surface. The cutting end of element
43 includes an inner end
63 and an outer end
65, the terms inner and outer being defined relative to the center line of bit body
13, inner being closer to the center line and outer being more distant from the center
line toward the sidewall of the borehole. A pair of flanks
67, which converge at an angle to define a crest
69, connect ends
63,
65 of element
43.
[0027] A portion of outer end or surface
65 of element
43 is formed of super-hard material
71, which is flush with crest
69 and defines a cutting edge
73 for shearing engagement with the sidewall of the borehole. Super-hard materials include
natural diamond, polycrystalline diamond, cubic boron nitride and similar materials
having hardnesses in excess of 2800 on the Knoop hardness scale. Super-hard materials
are to be distinguished from cemented carbide materials and other hard metals, and
are the materials used to cut, grind, and shape hard metals and other similar materials.
[0028] Preferably, as shown in Figure 3, super-hard material
71 is a polygonal wedge of polycrystalline diamond cut from a circular diamond table.
Wedge
71 is secured to element
43 by brazing, as disclosed in commonly assigned U.S. Patent No. 5,355,750, October
18, 1994 to Scott et al. Wedge
73 can also be formed integrally with element
43 in a high-pressure, high-temperature apparatus as disclosed in commonly assigned
U.S. Patent No. 5,355,750.
[0029] Figure 4 is an elevation view of another embodiment of a cutting element
143 according to the present invention. Unlike the embodiment of Figures 2 and 3, which
is generally chisel-shaped and easily permits definition of a cutting edge
73 of super-hard material
71, element
143 has an ovoid cutting end that does not clearly define inner and outer ends or flanks,
but does define a crest
169.
[0030] Element
143 has a flat outer surface
165 superimposed on the ovoid portion and adapted for engagement with the sidewall of
the borehole during drilling operation. A disk
171 of super-hard material projects beyond outer surface
165 and defines a cutting edge
173 for shear-cutting engagement with the sidewall of the borehole. Preferably, the cutting
edge projects no greater than 0.060 inch to avoid subjecting super-hard material
171 to excessive bending loads. The bevel of disk
171 provides a cutting or chip-breaking surface
175 that defines a negative rake angle with respect to the sidewall of the borehole.
In this embodiment, disk
171 is a portion of super-hard core or cylinder extending through element
143.
[0031] Figures 5 and 6 are elevation and plan views of a cutting element
243 according to the present invention. Cutting element
243 is of the chisel-shaped configuration and has a cylindrical body
261 formed of cemented tungsten carbide. Inner and outer surfaces
263, 265 and a pair of flanks
267 converge to define a crest
269 to avoid exposure to impact loads occurring at the crest. Outer surface
265 is machined flat in this embodiment. A beveled disk
271 of super-hard material projects beyond outer surface or end
265 and defines a cutting edge
273 for shearing engagement with the sidewall of the borehole that is recessed from crest
269. Disk
271 of super-hard material is beveled to provide a cutting or chip-breaking surface
275 that defines a negative rake angle with respect to the sidewall of the borehole during
drilling operation.
[0032] Figures 7 and 8 are elevation and plan views, respectively, of another cutting element
343 according to the present invention. Cutting element
343 is configured such that when cylindrical body
361 is secured by interference fit in an aperture in heel surface
41, crest
369 of cutting element
343 is oriented transversely to the axis of rotation of each cutter
21,
23,
25. Thus, flanks
363, 365 of cutting element
343 define the inner and outer surfaces of cutting element
343, rather than the ends in more conventional chisel-shaped cutting elements. These
larger surface areas are more wear-resistant that the smaller ends. A disk
371 of super-hard material is secured to outer flank
365 and defines a cutting edge
373 and cutting surface
375 for shearing engagement with the sidewall of the borehole.
[0033] Figures 9 and 10 are plan and elevation views, respectively, of another chisel-shaped
cutting element
443 according to the present invention. A pair of flanks
467 converge from cylindrical body
461 to define a crest
469 formed of the cemented tungsten carbide material of body
461. A crest or cutting edge
473 of super-hard material
471 is formed on the outer end
465 and is recessed almost to the intersection of body
461 and end
465. With this recess, cutting edge
471 and cutting surface
475 are positioned to scrape the sidewall of the borehole further from the corner and
bottom of the borehole, rendering cutting element
443 a more secondary cutting structure.
[0034] During drilling operation, bit
11 is rotated and cutters
21,
23,
25 roll and slide over the bottom of the borehole and the cutting elements crush, gouge,
and scrape the formation material. As heel elements
43,
143,
243,
343,
443 engage the sidewall of the borehole, super-hard cutting edges
73,
173,
273, 373, 473 scrape and shear formation material on the sidewall and in the corner of the borehole.
Scraper elements
51 and gage elements
33 further assist in scraping and shearing the sidewall and corner. The remainder of
super-hard material
71,
171,
271,
371, 471 on outer end or surface
65,
165,
265,
365,
465 of heel elements resists abrasive wear of this important area of cutting structure.
The fracture-tough metal of the remainder of the heel elements
43, 143 243, 343,
443 gives crest
69,
169,
269, 369,
469 and flanks
67, 167,
267,
367,
467 sufficient strength and toughness to withstand the impact loads encountered by the
cutting elements engaging the bottom of the borehole.
[0035] The earth-boring bit according to the present invention has a number of advantages.
A principal advantage is that the bit according to the present invention is provided
with a heel cutting structure that advantageously employs the shearing mode of formation
disintegration.
[0036] The invention has been described with reference to preferred embodiments thereof.
It is thus not limited, but is susceptible to modification and variation without departing
from the scope and spirit thereof.
1. An earth-boring bit comprising:
a bit body;
at least one cantilevered bearing shaft depending inwardly and downwardly from the
bit body;
a cutter mounted for rotation on the bearing shaft, the cutter including a plurality
of cutting elements arranged in generally circumferential rows on the cutter, the
generally circumferential rows including a heel row of cutting elements;
at least one of the cutting elements in the heel row having an outer surface at least
partially formed of super-hard material and defining a cutting edge for shearing engagement
with the sidewall of the borehole as the cutter rolls and slides over the bottom of
the borehole during drilling operation.
2. The earth-boring bit according to claim 1 wherein each cutting element in the heel
row is generally chisel-shaped and includes an inner end, an outer end, and a pair
of flanks converging to define a crest, a portion of the outer end being formed of
super-hard material extending to the crest of the cutting element to define a cutting
edge for shear cutting engagement with the sidewall of the borehole.
3. The earth-boring bit according to claim 1 wherein each cutting element in the heel
row is ovoid and the cutting edge of super-hard material is recessed from the crest.
4. The earth-boring bit according to claim 1 wherein each cutting element has a pair
of ends, and inner and outer flanks that converge to define a crest oriented transversely
to the rotational axis of the cutter, a portion of the outer flank being formed of
the super-hard material, and the cutting edge is recessed from the crest.
5. The earth-boring bit according to claim 1 wherein the super-hard material is polycrystalline
diamond and the remainder of the cutting element is formed of cemented tungsten carbide.
6. The earth-boring bit according to claim 1 wherein the cutting elements are secured
by interference fit into apertures in the cutter surface.
7. The earth-boring bit according to claim 1 wherein each cutting element in the heel
row is generally chisel-shaped and includes an inner end, an outer end, and a pair
of flanks converging to define a crest, a portion of the outer end being formed of
super-hard material to define a cutting edge recessed from the crest for shear cutting
engagement with the sidewall of the borehole.
8. The earth-boring bit according to claim 1 wherein each cutting element is provided
with a beveled cutting surface adjacent the cutting edge and formed of the super-hard
material.
9. The earth-boring bit according to claim 1 wherein the super-hard portion of the outer
surface projects beyond the remainder of the outer surface for engagement with the
sidewall of the borehole.
10. An earth-boring bit comprising:
a bit body;
at least one cantilevered bearing shaft depending inwardly and downwardly from the
bit body;
a cutter mounted for rotation on the bearing shaft, the cutter including a plurality
of cutting elements arranged in generally circumferential rows on the cutter, the
generally circumferential rows including a heel row of cutting elements;
at least one of the cutting elements in the heel row being having a plurality of surfaces
including an outer surface, a portion of the outer surface being formed of super-hard
material extending to and flush with the crest of the cutting element to define a
cutting edge for shear cutting engagement with the sidewall of the borehole during
drilling operation, the remainder of the surfaces of the cutting element being formed
of fracture-tough material.
11. The earth-boring bit according to claim 11 wherein each cutting element in the heel
row is generally chisel-shaped and includes an inner end, an outer end, and a pair
of flanks converging to define a crest, a portion of the outer end being formed of
super-hard material extending to and flush with the crest of the cutting element to
define a cutting edge for shear cutting engagement with the sidewall of the borehole.
12. The earth-boring bit according to claim 11 wherein the super-hard material is polycrystalline
diamond and the fracture-tough material is cemented tungsten carbide.
13. The earth-boring bit according to claim 11 wherein the cutting elements are secured
by interference fit into apertures in the cutter surface.
14. An earth-boring bit comprising:
a bit body;
at least one cantilevered bearing shaft depending inwardly and downwardly from the
bit body;
a cutter mounted for rotation on the bearing shaft, the cutter including a plurality
of cutting elements arranged in generally circumferential rows on the cutter, the
generally circumferential rows including a heel row of cutting elements;
at least one of the cutting elements in the heel row being formed of fracture-tough
material and having a crest and an outer surface, a portion of the outer surface being
formed of super-hard material to define a cutting edge for shear cutting engagement
with the sidewall of the borehole during drilling operation, the cutting edge being
recessed from the crest of the element.
15. The earth-boring bit according to claim 15 wherein the super-hard material is polycrystalline
diamond and the fracture-tough material is cemented tungsten carbide.
16. The earth-boring bit according to claim 15 wherein the cutting elements are secured
by interference fit into apertures in the cutter surface.
17. The earth-boring bit according to claim 15 wherein each cutting element in the heel
row is generally chisel-shaped and includes an inner end, an outer end, and a pair
of flanks converging to define a crest, a portion of the outer end being formed of
super-hard material to define a cutting edge recessed from the crest for shear cutting
engagement with the sidewall of the borehole.
18. The earth-boring bit according to claim 15 wherein each cutting element in the heel
row is ovoid and the cutting edge of super-hard material is recessed from the crest.
19. The earth-boring bit according to claim 15 wherein each cutting element has a pair
of ends, and inner and outer flanks that converge to define a crest oriented transversely
to the rotational axis of the cutter, a portion of the outer flank being formed of
the super-hard material, and the cutting edge is recessed from the crest.
20. The earth-boring bit according to claim 15 wherein the super-hard portion of the outer
surface projects beyond the remainder of the outer surface for engagement with the
sidewall of the borehole.
21. The earth-boring bit according to claim 15 further including a beveled cutting surface
formed adjacent the cutting edge and formed of the super-hard material.